In order to connect, for example, a to be driven attachment implement, to a power take-off shaft of a tractor, via a universal joint shaft, a proper procedure must be followed. Accordingly, during the coupling procedure of the universal joint shaft to the power take-off shaft, the universal joint shaft, not coupled yet, is aligned in relation to the power take-off shaft so that the universal joint shaft can be axially pushed, with its coupling portion, onto the splined power take-off shaft. This is often difficult to achieve. This is due to the fact that the attachment implements have a high mass to be accelerated which makes rotating the universal shaft by hand, to achieve the aligned position necessary for the coupling procedure, practically impossible. This also applies if the implement drive is blocked or if the tractor power take-off shaft is fixed by a brake.
To facilitate the coupling procedure, DE 44 45 634 C2 (=GB 22 96 308 A) proposes to connect two free wheel couplings one behind the other. The two coupling elements can be freely rotated in relation to each other about a limited rotational angle. This enables the components of the drive connection, for example the power take-off shaft and the coupling portion of a universal joint shaft, to be brought into a corresponding position. In a correspondingly formed splined shaft stub and bore of the coupling portion, the splines and gaps can be aligned such that an easy pushing-on and thus, coupling is possible. The size of the differences in pitch can be selected to provide a sufficiently large free rotational motion angle. This embodiment necessitates two free wheel couplings which increases the structural expenditure.
U.S. Pat. No. 5,681,222 A describes an overload frictional slip coupling with free motion in the rotational sense. The coupling has a coupling housing, a coupling hub and between the two a frictional arrangement for the transmission of torque. A universal joint yoke is fixed to the coupling housing. Both rotate together without fee rotational motion between the two. A rolling member bearing is arranged between the coupling hub and the universal joint yoke. The bearing retains both elements in relation to each other in a radial and axial direction. A coupling disc with a frictional lining is arranged between an end wall of the coupling housing and a pressure plate. The disc is connected to the coupling hub via projections and recesses. The disc enables a relative free rotational motion between the two. A disadvantage in this embodiment is that the free motion, in the rotational sense, is provided at components which form part of the frictional coupling. Such an embodiment is limited to frictional couplings.